SettingsLibTests: grant access to Wifi @hide APIs

Allow SettingsLib integration tests to access
@hide Wifi APIs.

This should only be temporary since WifiTracker
(and by extension WifiTrackerTest) will be
replaced by WifiTracker2.

Bug: 146513037
Test: atest SettingsLibTests
Test: m ANDROID_BUILDSPEC=vendor/google/build/app_build_spec.mk (build against git_master/apps target)
Change-Id: Iefcdaceafedaf4d3c07af2c1370b53d04539e88f